Devices for the detection of leaks in pipelines are well known and emply various scientific principles. Some employ the sound emitted as pressurized fluid escapes through a break in the pipe. Others utilize resultant sonic waves to detect at a distance from the break. Others utilized pressure drop in the immediate area of the leak, as does the present invention. However, known devices employing the pressure drop principle have either employed sealing rings to establish a chamber isolated from the stream, or have plugged the leak momentarily to provide a null indicative of the location of the leak. Since pipelines are seldom truly circular in cross section, sealing rings often fail. Cylindrical plugs of sound absorbing materials adapted to plug the leak present operational and maintenance problems not associated with the leak detectors disclosed herein.